The six "internal" genes of an additional avian influenza donor virus, A/Mallard/Alberta/88/76, attenuated the wild-type human influenza A/Korea/1/82 virus for humans. In terms of attenuation, safety, restriction of virus replication and immunogenicity, this avian-human influenza A reassortant virus was similar to the previously studied human-avian influenza A reassortant viruses produced using the avian influenza A/Mallard/NY/6750/78 donor virus. Studies with reassortant viruses which contain a single RNA segment derived from the influenza A/Ann Arbor/6/60 ca donor virus and all other RNA segments from the influenza A/Korea/82 virus confirm our hypothesis that the polymerase PA of the ca donor virus plays a major role in the transfer of the ca and attenuation phenotypes. These studies indicate that the attenuation specified by the polymerase PA is due to a mechanism other than temperature sensitivity. Nasal wash HA specific IgG antibody detected in volunteers who received live or inactivated influenza A vaccines was derived as a transudate from serum. The minimum serum HA specific IgG ELISA titer required to produce detectable nasal wash antibody, 1:350, is similar to the level of transplacentally-derived serum neutralizing antibody that is associated with resistance to another virus, respiratory syncytial virus.